A dobson unit is the most basic measure used in ozone research. The unit is named after G.M.B. Dobson, one of the first scientists to investigate atmospheric ozone (~1920 - 1960). He designed the 'Dobson Spectrometer' - the standard instrument used to measure ozone from the ground. The Dobson spectrometer measures the intensity of solar UV radiation at four wavelengths, two of which are absorbed by ozone and two of which are not.

The illustration above shows a column of air, 10 deg x 5 deg, over Labrador, Canada. The amount of ozone in this column (i.e. covering the 10 x 5 deg area) is conveniently measured in Dobson Units.

If all the ozone in this column were to be compressed to stp (0 deg C and 1 atmosphere pressure) and spread out evenly over the area, it would form a slab approximately 3mm thick.

1 Dobson Unit (DU) is defined to be 0.01 mm thickness at stp; the ozone layer over Labrador then is ~300 DU.

NOTE: This page, including the copyrighted graphic, is based on a page developed by Owen Garrett for the Centre for Atmospheric Science at Cambridge University, UK. The center has kindly given us permission to reproduce it. (Take their excellent Multimedia Ozone Hole Tour!)